Denitrification process and system

ABSTRACT

The disclosed process and system are used for the denitrification of wastewater. The system comprises: an influent concentration analyzer for measuring an influent dissolved oxygen concentration, an influent nitrate concentration, and an influent nitrite concentration; and a feed chemical controller for providing a feed chemical at a controlled rate. The feed chemical controller is responsive to one or more output signals provided by an automated control loop that accepts input signals from the influent concentration analyzer, which input signals relate to at least two of the influent nitrate concentration, the influent nitrite concentration, and the influent dissolved oxygen concentration

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application is a Divisional of U.S. application Ser. No.12/694,768, filed Jan. 27, 2010, which is a Continuation of U.S.application Ser. No. 12/246,169, filed Oct. 6, 2008 (now U.S. Pat. No.7,662,287), which is a Divisional of U.S. application Ser. No.11/504,101, filed Aug. 15, 2006 (now U.S. Pat. No. 7,431,840), whichclaims priority to U.S. Provisional Application No. 60/710,612, filedAug. 24, 2005, the disclosures of which are incorporated by referenceherein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a system and process forwastewater treatment and, in particular, to a system and process fordenitrification of wastewater.

2. Related Art

According to a recent article, which appeared in the Washington Post(“Troubled Waters in the Shenandoah: Death of Smallmouth Bass BringsAttention But No Quick Answers on Improving Quality” By Michael AlisonChandler, Washington Post Staff Writer, Wednesday, Jul. 20, 2005; PageB01), questions are constantly being raised about the quality of thewater that feeds into waterways in and around the Shenandoah Valley and,ultimately, the Chesapeake Bay. Among the factors cited in the article,the high nutrient (and nitrogen) content in the feed waters was noted asa significant culprit:

-   -   The river is also known to have high nutrient levels. Nitrogen        and phosphorus in high amounts cause excess plant or algae        growth, which can reduce levels of dissolved oxygen. Fish        struggle to breathe, and that can weaken their resistance to        disease or bacteria.    -   The land along all three rivers affected by the fish kills is        primarily agricultural. With more than 900 farms in the valley,        the poultry industry dominates. High-nutrient waste from the        farms is used as fertilizer and can wash into the river.        It is clear that better, more effective ways to control the        nitrogen content of waste water are needed.

It is known, that the control of feed chemicals used in the processingof liquids (e.g., waste water in a waste water treatment system) can beautomated through the use of computerized control devices. Problems canoccur during the automatic dosing of chemicals into the treatment systembecause of inaccuracies of measurements of a chemical present in thesystem and the variable ratio of chemical to liquid when the liquid flowrate is variable.

In the past, dosing was done by laboratory or bench testing the influentchemical concentration, in combination with influent flow ratemeasurements. Subsequently, dose calculations were performed and thedosing device, a chemical feed pump, for example, was manually adjustedaccording to the calculations. More recently, partial pacing of thedosing pumps was practiced using an influent water flow signal. Varyingthe dose rate to maintain a desired effluent chemical concentration testresult was deemed a more direct approach.

In recent years, reliable automatic analyzers for chemical concentrationhave become available, thus enabling automation of the entire dosingprocedure. Automatic analyzers can also be set up to detect severalimportant chemicals in waste water treatment system, enabling the use ofa variety of chemicals depending on the specific application, e.g., theaddition of sodium bicarbonate into an aerated biological reactor or theaddition of iron or aluminum salts before a clarifier to controlphosphorus removal.

In U.S. Pat. No. 6,129,104 (the '104 patent), the contents of which areincorporated herein by reference, a method for controlling the additionof liquid treatment chemicals by automatic dose control is provided. Inthis method, the calculation of the amount of chemical to be dosed intothe system combines signals from a liquid flow meter, an influentchemical concentration analyzer, and an effluent chemical concentrationanalyzer. The signals are directed to a computerized chemical dosecontroller that analyzes and adjusts the data from the signals andgenerates an output signal that controls the chemical dosing mechanisms.According to the '104 patent, this method may be used, for example, fordenitrification of wastewater using methanol as the feed chemical.

Denitrification comprises the removal of nitrate and nitrite from awaste stream through the use of facultative heterotrophic bacteria.These facultative heterotrophic bacteria, in the presence of a carbonsource (e.g., methanol), and in the absence of dissolved oxygen (DO),can strip the oxygen atoms from both nitrate and nitrite moieties,leaving nitrogen gas (N₂), which exits the waste stream and enters theatmosphere (air is about eighty percent nitrogen gas), hence“denitrifying” the waste stream. Thus, methanol consumption is dependenton influent nitrate and nitrite as well as influent DO, namely, enoughmethanol is required to first deplete the influent DO and subsequentlyto account for stripping all the oxygen atoms associated with nitrateand nitrite.

The '104 patent, however, ignores DO and nitrites and further describesmeasuring influent and effluent concentrations of nitrates only in orderto determine an amount of methanol to be fed into the system fordenitrification. However, as discussed above, the measurement of theinfluent and effluent concentrations of nitrates is insufficient indetermining the proper amount of methanol to be fed into the system fordenitrification. Stated another way a methanol dosing system thatstrictly looks at influent and effluent nitrate would not account formethanol demands associated with varying levels of influent nitrite andDO, thus leading to possible overdosing or underdosing of methanol. Forexample, relying on influent nitrate measurements only can result inoverdosing because of a drop in influent DO levels. By the same token,reliance on effluent nitrate measurements can result in underdosingbecause a low level of measured effluent nitrate misses altogether thefact that a reduction in nitrate levels can simply mean that all thenitrate has been converted to nitrite, which must still be reduced. Thatis, nitrate is first converted to nitrite (thus leading to an increasein the levels of nitrite) on the way to complete conversion to gaseousnitrogen. Instead, the '104 patent relies on “fudge” factors, forinstance, the use of an “adjustable factor [which] is determined by theoperator” and/or the use of a “sensitivity factor [which] is selected bythe operator” to compensate for the inaccuracy inherent in limitingmeasurements to nitrate concentrations. Initially theseoperator-controlled “factors” are no more than educated guesses and, atbest, might be derived empirically. Implicit in such anoperator-controlled technique is the necessity for an operator to “getup to speed” on system requirements, all of which represents a timeconsuming “learning curve.”

Therefore, there is a need for a more accurate, automated method ofdetermining an amount of feed chemical (e.g., methanol) to be fed into adenitrification system without reliance on operator-controlledadjustable or sensitivity factors. In particular, there is a need for amethod that takes influent concentrations of nitrogen-containingsubstances, in addition to nitrates (e.g., nitrites) (so called NO_(x)),and dissolved oxygen and effluent concentrations of thesenitrogen-containing substances (i.e., NO_(x)) into account incalculating the proper dose of feed chemical. These measurements can betaken either from influent samples only or from both influent andeffluent samples.

SUMMARY OF INVENTION

In one aspect, the invention provides an aqueous denitrification processfor a wastewater treatment system. The wastewater treatment system hasinfluent and effluent aqueous flows, a filtration bed harboringmicrobes, and feed forward and optional feed back control loops. Theprocess comprises the steps of: a) determining influent flow (optionallyexpressed in millions of gallons per day), Q, influent dissolved oxygenconcentration (optionally expressed in mg/liter), DO_(in), influentnitrate concentration (optionally expressed in mg/liter), NO₃—N_(in),and influent nitrite concentration (optionally expressed in mg/liter),NO₂—N_(in); b) utilizing a feed forward control loop relationship (1) todetermine a feed chemical requirement, FCR,

FCR=Q[(X*DO)+(Y*NO₃—N_(in))+(Z*NO₂—N_(in))]  (1)

in which X, Y, and Z are predetermined unitless factors ranging fromabout 0.7 to about 3.0; c) optionally determining effluent nitrateconcentration (optionally expressed in mg/liter), NO₃—N_(eff), andeffluent nitrite concentration (optionally expressed in mg/liter),NO₂—N_(eff); and d) optionally utilizing feed back control looprelationships (2), (3) and (4) to determine an adjusted feed chemicalrequirement, AFCR, utilizing relationship (5),

$\begin{matrix}{{AP} = {{GAIN}*{ERR}}} & (2) \\{{AI}_{({new})} = {{AI}_{({old})} + {{GAIN}*\frac{dl}{TI}*\frac{{ERR}_{({new})} + {ERR}_{({old})}}{2}}}} & (3) \\{A = {{AP} + {AI}}} & (4) \\{{A\; F\; C\; R} = {F\; C\; R*\left( {1 + A} \right)}} & (5)\end{matrix}$

in which GAIN is a predetermined unitless action coefficient, ERR is thedifference between measured NO_(x)—N_(eff) (which is the sum ofNO₃—N_(eff) and NO₂—N_(eff)) and set point NO_(x)—N_(eff), dl is the sumof the microprocessor processing time (optionally expressed in seconds)and a time interval, TI (optionally expressed in seconds), betweenmeasurements, and references to new and old refer to a currentmeasurement and a prior measurement. The value of FCR may be expressedin pounds per day by multiplying the value for FCR obtained viarelationship (1) by a conversion factor, which is 8.34. The values forX, Y and Z are determined by the stoichiometric equation for theconsumption of dissolved oxygen, nitrates and nitrites in the presenceof methanol. A more detailed discussion of preferred embodiments ispresented, below. However, in one embodiment of the invention, the valueof X may be set, for example, at 0.81, the value of Y may be set, forexample, at 2.25, and the value of Z may be set, for example, at 1.35.The value of GAIN may be set, for example, at 0.2. The value of TI maybe set, for example, at 400 seconds. The value of set pointNO_(x)—N_(eff) may fall within the range of 0.25 mg/liter to 10.0mg/liter. The quotient dl/TI may be approximately equal to 1. The valuesfor AI_((old)) and ERR_((old)) may be set at the initial measurement to0. It should be emphasized, however, that the invention is not limitedto or by the equations provided above, which simply serve asillustrative of a preferred embodiment of the invention.

In another aspect of the invention, a wastewater denitrification systemis provided. The system comprises an influent flow meter for measuringan influent flow (optionally expressed in millions of gallons per day),Q; an influent concentration analyzer for measuring an influentdissolved oxygen concentration (optionally expressed in mg/liter),DO_(in), an influent nitrate concentration (optionally expressed inmg/liter), NO₃—N_(in), and an influent nitrite concentration (optionallyexpressed in mg/liter), NO₂—N_(in); an optional effluent concentrationanalyzer for measuring an effluent nitrate concentration (optionallyexpressed in mg/liter), NO₃—N_(eff), and an effluent nitriteconcentration (optionally expressed in mg/liter), NO₂—N_(eff); and afeed chemical controller for providing a feed chemical at a controlledrate. The feed chemical controller is responsive to one or more outputsignals provided by an automated control loop that accepts input signalsfrom the influent concentration analyzer and optionally the effluentconcentration analyzer. The input signals relate to at least NO₃—N_(in)and NO₂—N_(in) and, optionally, NO₃—N_(eff), and NO₂—N_(eff). Theautomated control loop may also accept input signals relating toDO_(in). The automated control loop may also accept input signalsrelating to Q. The feed chemical may be provided as part of the influentflow. The feed chemical may include any source of carbon, including butnot limited to acetic acid, sugars, methanol, ethanol, and the like. Theautomated control loop may be configured to accept input signals at apredetermined time interval, TI.

In yet another aspect of the invention, a method of automaticallycontrolling a rate at which a feed chemical is provided to microbesharbored in a filtration bed is provided. The method comprises the stepsof: (i) determining an influent flow rate (optionally expressed inmillions of gallons per day), Q, an influent dissolved oxygenconcentration (optionally expressed in mg/liter), DO_(in), an influentnitrate concentration (optionally expressed in mg/liter), NO₃—N_(in),and an influent nitrite concentration (optionally expressed inmg/liter), NO₂—N_(in); (ii) determining a feed chemical requirement,FCR, based in part on the values for Q, DO_(in), NO₃—N_(in), andNO₂—N_(in), obtained from step (i); (iii) optionally determining aneffluent nitrate concentration (optionally expressed in mg/liter),NO₃—N_(eff), and an effluent nitrite concentration (optionally expressedin mg/liter), NO₂—N_(eff); (iv) optionally determining an adjusted feedchemical requirement, AFCR, based in part on the values for NO₃—N_(eff)and NO₂—N_(eff), obtained from step (iii) (that is, NO_(x)—N_(eff)), andERR, which is the difference between measured NO_(x)—N_(eff) (which, inturn, is the sum of NO₃—N_(eff) and NO₂—N_(eff)) and set pointNO_(x)—N_(eff); and (v) repeating steps (i), (ii), (iii), and (iv) at apredetermined time interval, TI.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a denitrification system according to apreferred embodiment of the invention.

FIG. 2 is a flow chart that illustrates a method for calculating adosage of methanol to be provided to a denitrification system accordingto a preferred embodiment of the invention.

FIG. 3 is a color/shaded plot of the diurnal variations found forinfluent concentrations of influent nitrate, influent phosphate andinfluent dissolved oxygen.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a system and method for performingdenitrification of a liquid flow, typically wastewater. Unlikeconventional denitrification systems, which rely exclusively on themeasurement of influent and effluent concentrations of nitrates toassist in a calculation of a dosage of a feed chemical, typicallymethanol, and requires an experienced operator to determine “adjustable”and “sensitivity” factors to “fudge” feed chemical dosage values, thepresent invention also includes the advantages of measuring influent andeffluent concentrations of nitrites, as well as the influentconcentration of dissolved oxygen, in order to determine a more accuratedosage of methanol to be used in the wastewater treatment process.Hence, no operator-controlled factors are required, as discussed furtherherein. The invention also encompasses a system in which effluentmeasurements are merely optional, thus reducing system complexity andcost.

Referring to FIG. 1, a block diagram of a denitrification system 100according to a preferred embodiment of the invention is shown. Thesystem 100 accepts an influent flow 105 of a liquid to be treated,typically wastewater. The influent flow 105 first encounters an influentflow meter 110, which measures a flow rate of the liquid, and generatesa flow rate signal corresponding to the measurement. The influent flow105 then continues to an influent concentration analyzer 115. Theanalyzer 115, which may comprise one or more devices, measuresconcentrations of nitrates, nitrites, and dissolved oxygen within theinfluent flow, and generates signals corresponding to each of theseinfluent concentrations. These signals can then be combined, along withthe flow rate signal, to provide a control signal. Then, the influentflow 105 continues into the treatment process 120. The treatment process120 treats the wastewater.

The treatment process 120 may include a filter system. For example, asand filter system may be used to filter out solid materials from thewastewater. In one preferred embodiment, one or multiple continuousbackwash upflow sand filter systems may be used within the treatmentprocess 120. See, U.S. Pat. Nos. 4,126,546, 4,197,201, and 4,246,102 forexamples of suitable sand filtration systems. The disclosures of thesepatents are incorporated by reference herein.

One aspect of the treatment process 120 is a denitrification of thewastewater. Denitrification is accomplished by providing a feedchemical, typically methanol, to the wastewater. As described, above,microbes harbored in the filtration bed consume the methanol along withthe nitrates and nitrites that are present in the wastewater to producegaseous nitrogen, which then diffuses naturally into the ambientatmosphere. In this manner, a substantial amount of the nitrogen contentin the wastewater is eliminated, hence the term “denitrification.”

In a preferred embodiment of the invention, methanol is chosen as thefeed chemical because of its availability and cost relative to othersynthetic feed chemicals. Its presence in the downstream effluent mustnevertheless be held to a minimum. Thus the present invention seeks toprovide a more accurate determination of the amount of methanol requiredto accomplish the desired levels of denitrification, yet not provide anexcess of methanol, whose presence in the effluent might proveproblematic.

It is known that the methanol introduced into the denitrification systemfirst consumes the dissolved oxygen present in the influent, accordingto the equation: 3O₂+2CH₃OH=2CO₂+4H₂O. Subsequently, reduction ofnitrate and nitrite transpires. Each transformation can be described bythe following stoichiometric equations: 6NO₃ ⁻+5CH₃OH=3N₂+5CO₂+7H₂O+6OH⁻and 2NO₂ ⁻+CH₃OH═N₂+CO₂+H₂O+2OH⁻. The nitrogen gas produced diffusesinto the atmosphere. Accordingly, stoichiometric amount of methanolrequired for complete denitrification is provided by the equation:CH₃OH=0.7DO+2.0NO₃—N+1.1NO₂—N, in which methanol, influent dissolvedoxygen, influent nitrate and influent nitrite are expressed in mg/L.Actual values for X, Y and Z can be chosen at the outset, but can bechanged at a later time if desired. Actual values are likely to be acertain percentage in excess of stoichiometric needs.

After the treatment process 120 is complete, the treated wastewater thenencounters an optional effluent concentration analyzer 125. The analyzer125 optionally measures concentrations of nitrates and nitrites presentin the effluent flow 130, which then exits the filtration system. Theanalyzer 125 can also generate signals that respectively correspond tothe effluent nitrate and nitrite concentrations.

A critical aspect of the denitrification system 100 is the determinationof the amount of the methanol dosage to be fed into the treatmentprocess 120. In order to optimize system efficiency, the calculatedamount should be as accurate as possible. The present invention providesan improved accuracy by measuring multiple analytes, which provide amore complete picture of the amount of feed chemical required.

Referring to FIG. 2, a flow chart 200 illustrates a methodology forcalculating an amount of methanol to be fed into the treatment process120. First, at step 205, the influent flow rate is measured using theinfluent flow meter 110. A flow rate signal is generated from this firstmeasurement, and may be represented by the variable Q, and typicallyexpressed in millions of gallons per day. In the second step 210,measurements are taken for the influent concentrations of nitrates,nitrites, and dissolved oxygen, and corresponding signals are generated.These signals are typically expressed in units of milligrams per liter(mg/L), and may be represented by the following variables: Influentconcentration of dissolved oxygen=DO_(in); influent concentration ofnitrates=NO₃—N_(in); and influent concentration of nitrites=NO₂—N_(in).

Then, at step 215, the generated signals are used to calculate a nominalvalue of the feed chemical requirement (FCR) according to Equation 1below:

FCR=Q[(X*DO_(in))+(Y*NO₃—N_(in))+(Z*NO₂—N_(in))]  (1)

where X, Y, and Z are predetermined unitless factors that typically fallwithin the range of 0.7 to 3.0. As discussed above, the stoichiometricamount of methanol needed for complete denitrification requires thatX=0.7, Y=2.0 and Z=1.1. These are the minimum values. However, onetypically requires an excess of methanol to drive the stoichiometricreaction to completion. Hence, an excess of methanol, up to 50% inexcess of stoichiometric requirements, may be desired. Typically, a10-30% percent excess might be desired, preferably 15-20% excess. In oneembodiment of the invention, therefore, X=0.9, Y=2.5 and Z=1.5. In yetanother embodiment of the invention X=0.8, Y=2.3, and Z=1.4. The valueof FCR may be converted to units of pounds per day by multiplying theinitial value by the conversion factor, 8.34.

At step 220, optional measurements are taken from the effluent flow ofthe concentrations of nitrates and nitrites. Once again, signals aregenerated that correspond to these measurements. These signals may berepresented by the following variables: Effluent concentration ofnitrates=NO₃—N_(eff); and effluent concentration ofnitrites=NO₂—N_(eff); and total effluent concentration of nitrates andnitrites=NO₃—N_(eff)+NO₂—N_(eff)═NO_(x)—N_(eff). These signals (namely,NO_(x)—N_(eff)) are then used to calculate an optional adjustment to thenominal FCR value at step 225. The entire method according to the flowchart 200 is then repeated continuously so that the methanol value iscontinuously updated in conjunction with the continuous influent flow.

In a preferred embodiment of the invention, the adjustment to the FCRvalue is determined through the use of an optional feedback process thatuses a proportional-integral (PI) loop. The adjustment A includes aproportional component AP and an integral component AI; hence, A=AP+AI.The proportional component AP is defined by Equation 2 below:

AP=GAIN*ERR  (2)

where GAIN=the desired magnitude of reaction as a function of theperceived error, and ERR=system deviation=the difference between theeffluent set point and the process value. The effluent set point is theexpected value of the total effluent concentration of nitrates andnitrites, and the process value is the actual, measured total value ofthe effluent concentration of nitrates and nitrites. Typically, theeffluent set point falls within a range of 0.25 mg/L to 10.0 mg/L. So,for example, if at a given time, the effluent set point is 0.5 mg/L, theactual measured effluent concentration of nitrates is 0.5 mg/L, and theactual measured effluent concentration of nitrites is 0.4 mg/L, then thetotal effluent concentration of nitrates and nitrites is 0.5 mg/L+0.4mg/L=0.9 mg/L, and thus ERR=0.9 mg/L−0.5 mg/L=0.4 mg/L. A typical valuefor GAIN could be 0.2. Thus, in this example, AP=0.2*0.4=0.08.

The integral component of the adjustment, AI, is defined according toEquation 3 below:

$\begin{matrix}{{AI}_{({new})} = {{AI}_{({old})} + {{GAIN}*\frac{dl}{TI}*\frac{{ERR}_{({new})} + {ERR}_{({old})}}{2}}}} & (3)\end{matrix}$

TI=Time Interval, or Reset Time=a predetermined time interval betweensuccessive measurements. For example, TI may be set equal to 400seconds. dl=Current Scan Time=an internal system function that tracksthe time required to perform the function from the moment the systemreceives all of the process variables. The Current Scan Time dl is a sumof TI and the actual computation time, which is typically on the orderof milliseconds, for example, approximately 20 ms. Thus, in thisexample, dl=400 s+20 ms=400.020 s. Therefore, the quotient dl/TIgenerally is approximately equal to 1, but it is always slightly greaterthan 1, never exactly equal to 1. The subscripts “new” and “old” referto the present and previous calculations, respectively. Thus, if a valueof the integral component AI is being calculated at present, i.e.,AI_((new)), then AI_((old)) refers to the value of AI that wascalculated 400 seconds ago.

Initial values of AI_((old)) and ERR_((old)) are generally set to zero.So, if all example values above are inserted into Equation 3, thefollowing result is obtained: AI_((new))=0+0.2*(400.020/400)*[(0.5)*(0.4mg/L+0)]=0.040002 mg/L=approximately 0.04 mg/L. Thus, the totaladjustment A=AP+AI=0.08+0.04=0.12.

The total adjustment value A may be limited in order to ensure thatadjustments do not exceed a predetermined maximum adjustment. Forexample, if a particular measurement deviates significantly from thetrend of previous measurements, it could be deemed an outlier or anerroneous measurement. Limiting the maximum amount of any givenadjustment accounts for such an outlier. In step 225, utilizing equation5, AFCR is calculated to be AFCR=FCR*(1+0.12) or a 12% increase overFCR.

Turning now to FIG. 3, the reader's attention is directed to a verysurprising, unexpected result of measuring influent nitrates (red/grayblocks), influent phosphates (navy/black diamonds) and influentdissolved oxygen (light blue/light gray blocks) over a twenty-four hourperiod. As shown in the figure, the concentration (in mg/L) of influentnitrate decreases from an average initial value of about 5.0 mg/L to lowaverage midday value of about 4.0 mg/L before rising again a few hoursprior to midnight to a high average value of about 5.5 mg/L. Quiteunexpectedly, influent dissolved oxygen steadily rises to reach a peakmidday value of about 2.7 mg/L before falling off sharply over the nextfive hours. Thus the concentrations of influent nitrates and influentdissolved oxygen traveled in opposite directions. An operator measuringthe concentration of only influent nitrates, even by resorting to“adjustable” or “sensitivity” factors, could not have accounted for anunexpected rise in influent dissolved oxygen and, thus, would have morethan likely underestimated the proper amount of methanol required toachieve the desired level of denitrification.

While the present invention has been described with respect to what ispresently considered to be the preferred embodiment, it is to beunderstood that the invention is not limited to the disclosedembodiments. To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

1. An aqueous denitrification process for a wastewater treatment system having influent and effluent aqueous flows and a filtration bed harboring microbes, the process comprising: determining an influent dissolved oxygen concentration, an influent nitrate concentration, and an influent nitrite concentration of wastewater; utilizing the dissolved oxygen concentration, the influent nitrate concentration, and the influent nitrite concentration to determine a feed chemical requirement; and providing a feed chemical to the wastewater based on the feed chemical requirement.
 2. The aqueous denitrification process of claim 1, further comprising determining influent flow, in which the feed chemical requirement is determined utilizing a feed forward control loop relationship, FCR=Q[(X*DO_(in))+(Y*NO₃—N_(in))+(Z*NO₂—N_(in)], and in which FCR is the feed chemical requirement, DO_(in) is the influent dissolved oxygen concentration, NO₃—N_(in) is the influent nitrate concentration, NO₂—N_(in) is the influent nitrite concentration, and X, Y, and Z are predetermined unitless factors ranging from about 0.7 to about 3.0.
 3. The aqueous denitrification process of claim 2, in which values of X, Y and Z are set to stoichiometric values.
 4. The aqueous denitrification process of claim 2, in which values of X, Y and Z are set 15% above stoichiometric values.
 5. The aqueous denitrification process of claim 2, in which values of X, Y and Z are set 30% above stoichiometric values.
 6. The aqueous denitrification process of claim 2, further comprising: determining an effluent nitrate concentration and an effluent nitrite concentration of the waste water; utilizing the effluent nitrate concentration and the effluent nitrite concentration to determine an adjusted feed chemical requirement; and providing the feed chemical to the wastewater based on the adjusted feed chemical requirement.
 7. The aqueous denitrification process of claim 6, in which the adjusted feed chemical requirement is determined utilizing the following relationships, AP = GAIN * ERR ${AI}_{({new})} = {{AI}_{({old})} + {{GAIN}*\frac{dl}{TI}*\frac{{ERR}_{({new})} + {ERR}_{({old})}}{2}}}$ A = AP + AI A F C R = F C R * (1 + A) in which FCR is the feed chemical requirement, AFCR is the adjusted feed chemical requirement, GAIN is a predetermined unitless action coefficient, ERR is a difference between measured NO_(x)—N_(eff) and set point NO_(x)—N_(eff), in which the measured NO_(x)—N_(eff) is a sum of the effluent nitrate concentration and effluent nitrite concentration, dl is a sum of microprocessor processing time and a time interval TI between measurements, and references to new and old refer to a current measurement and a prior measurement.
 8. The aqueous denitrification process of claim 6, in which GAIN is set at 0.2.
 9. The aqueous denitrification process of claim 6, in which TI is set at 400 seconds.
 10. The aqueous denitrification process of claim 6, in which the set point NO_(x)—N_(eff) falls within a range of 0.25 mg/liter to 10.0 mg/liter.
 11. The aqueous denitrification process of claim 6, in which dl/TI is approximately equal to
 1. 12. A method of automatically controlling a rate at which a feed chemical is provided to microbes harbored in a filtration bed comprising: (i) determining an influent dissolved oxygen concentration, an influent nitrate concentration, and an influent nitrite concentration; (ii) determining a feed chemical requirement based in part on the values for the influent dissolved oxygen concentration, the influent nitrate concentration, and the influent nitrite concentration, obtained from step (i); and repeating steps (i) and (ii) at a predetermined time interval.
 13. The method of claim 12, further comprising: (iii) determining an effluent nitrate concentration and an effluent nitrite concentration; (iv) determining an adjusted feed chemical requirement based in part on values for the effluent nitrate concentration and the effluent nitrite concentration, obtained from step (iii); and repeating steps (i), (ii), (iii), and (iv) at the predetermined time interval. 